Methods of bonding of semiconductor elements to substrates, and related bonding systems

ABSTRACT

A bonding system for bonding a semiconductor element to a substrate is provided. The bonding system includes a substrate oxide reduction chamber configured to receive a substrate. The substrate includes a plurality of first electrically conductive structures. The substrate oxide reduction chamber is configured to receive a reducing gas to contact each of the plurality of first electrically conductive structures. The bonding system also includes a substrate oxide prevention chamber for receiving the substrate after the reducing gas contacts the plurality of first electrically conductive structures. The substrate oxide prevention chamber has an inert environment when receiving the substrate. The bonding system also includes a reducing gas delivery system for providing a reducing gas environment during bonding of a semiconductor element to the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 16/736,416 filed on Jan. 7, 2020, which claims the benefit ofU.S. Provisional Application No. 62/790,259, filed Jan. 9, 2019, and ofU.S. Provisional Application No. 62/907,562, filed Sep. 28, 2019, thecontents of each of which are incorporated herein by reference.

FIELD

The invention relates to bonding systems and processes (such as flipchip, thermocompression, and thermosonic bonding systems and processes),and more particularly, to improved systems and methods for bonding asemiconductor element to a substrate.

BACKGROUND

Traditional semiconductor packaging typically involves die attachprocesses and wire bonding processes. Advanced semiconductor packagingtechnologies (e.g., flip chip bonding, thermocompression bonding, etc.)technologies continue to gain traction in the industry. For example, inthermocompression bonding (i.e., TCB), heat and/or pressure (andsometimes ultrasonic energy) are used to form a plurality ofinterconnections between (i) electrically conductive structures on asemiconductor element and (ii) electrically conductive structures on asubstrate.

In certain flip chip bonding or thermocompression bonding applications,the electrically conductive structures of the semiconductor elementand/or the substrate may include copper structures (e.g., copperpillars) or other material(s) that is subject to oxidation and/or othercontamination. In such applications, it is desirable to provide anenvironment suitable for bonding. Conventionally, such an environmentmay be provided by using a reducing gas at the bonding area to reducepotential oxidation and/or contamination of the electrically conductivestructures of the semiconductor element or the substrate to which itwill be bonded.

Thus, it would be desirable to provide improved methods of bondingsemiconductor elements to a substrate with the use of a reducing gas.

SUMMARY

According to an exemplary embodiment of the invention, a bonding systemfor bonding a semiconductor element to a substrate is provided. Thebonding system includes a substrate oxide reduction chamber configuredto receive a substrate. The substrate includes a plurality of firstelectrically conductive structures. The substrate oxide reductionchamber is configured to receive a reducing gas to contact each of theplurality of first electrically conductive structures. The bondingsystem also includes a substrate oxide prevention chamber for receivingthe substrate after the reducing gas contacts the plurality of firstelectrically conductive structures. The substrate oxide preventionchamber has an inert environment when receiving the substrate. Thebonding system also includes a reducing gas delivery system forproviding a reducing gas environment during bonding of a semiconductorelement to the substrate. The semiconductor element includes a pluralityof second electrically conductive structures. The plurality of firstelectrically conductive structures are configured to be bonded withcorresponding ones of the plurality of second electrically conductivestructures.

According to another exemplary embodiment of the invention, a method ofbonding a semiconductor element to a substrate is provided. The methodincludes the steps of: moving a substrate into a substrate oxidereduction chamber, the substrate including a plurality of firstelectrically conductive structures, the substrate oxide reductionchamber configured to receive a reducing gas to contact each of theplurality of first electrically conductive structures; moving thesubstrate into a substrate oxide prevention chamber after the reducinggas contacts the plurality of first electrically conductive structures,the substrate oxide prevention chamber having an inert environment whenreceiving the substrate; and providing a reducing gas environment duringbonding of a semiconductor element to the substrate, the semiconductorelement including a plurality of second electrically conductivestructures, the plurality of first electrically conductive structuresbeing configured to be bonded with corresponding ones of the pluralityof second electrically conductive structures.

According to yet another exemplary embodiment of the invention, a methodof bonding a semiconductor element to a substrate is provided. Themethod includes the steps of: (a) carrying a semiconductor element witha bonding tool of a bonding machine, the semiconductor element includinga plurality of first electrically conductive structures; (b) supportinga substrate with a support structure of the bonding machine, thesubstrate including a plurality of second electrically conductivestructures; (c) providing a reducing gas in contact with each of theplurality of first electrically conductive structures and the pluralityof second electrically conductive structures; and (d) bonding thecorresponding ones of the plurality of first electrically conductivestructures to the respective ones of the plurality of secondelectrically conductive structures after step (c). At least one of theplurality of first electrically conductive structures and the pluralityof second electrically conductive structures includes a solder material.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity.

FIG. 1A is a block diagram illustration of a bonding system for bondinga semiconductor element to a substrate in accordance with an exemplaryembodiment of the invention;

FIG. 1B is a block diagram illustration of a bonding system for bondinga semiconductor element to a substrate in accordance with an exemplaryembodiment of the invention;

FIGS. 2A-2G are a series of block diagram illustrations of the bondingsystem of FIG. 1A, illustrating a method of bonding a semiconductorelement to a substrate in accordance with an exemplary embodiment of theinvention;

FIGS. 3A-3B are a series of block diagram illustrations of the bondingsystem of FIG. 1A, illustrating a method of bonding a semiconductorelement to a substrate in accordance with an exemplary embodiment of theinvention, while preparing another substrate for bonding;

FIG. 4 is a block diagram illustration of a bonding system for bonding asemiconductor element, having conductive structures including a soldermaterial, to a substrate in accordance with an exemplary embodiment ofthe invention;

FIG. 5 is a block diagram illustration of a bonding system for bonding asemiconductor element to a substrate, having conductive structuresincluding a solder material, in accordance with an exemplary embodimentof the invention;

FIG. 6 is a block diagram illustration of a bonding system for bonding asemiconductor element, having conductive structures including a soldermaterial, to a substrate, having conductive structures including asolder material, in accordance with an exemplary embodiment of theinvention;

FIG. 7 is a block diagram illustration of a bonding system for bonding asemiconductor element, having conductive structures formed of a soldermaterial, to a substrate in accordance with an exemplary embodiment ofthe invention;

FIG. 8 is a block diagram illustration of a bonding system for bonding asemiconductor element to a substrate, having conductive structuresformed of a solder material, in accordance with an exemplary embodimentof the invention;

FIG. 9 is a block diagram illustration of a bonding system for bonding asemiconductor element, having conductive structures formed of a soldermaterial, to a substrate, having conductive structures formed of asolder material, in accordance with an exemplary embodiment of theinvention;

FIGS. 10A-10D are a series of block diagram illustrations of the bondingsystem of FIG. 4, illustrating a method of bonding a semiconductorelement to a substrate in accordance with an exemplary embodiment of theinvention; and

FIGS. 11A-11D are a series of block diagram illustrations of anotherbonding system, illustrating a method of bonding a semiconductor elementto a substrate in accordance with an exemplary embodiment of theinvention.

DETAILED DESCRIPTION

As used herein, the term “semiconductor element” is intended to refer toany structure including (or configured to include at a later step) asemiconductor chip or die. Exemplary semiconductor elements include abare semiconductor die, a semiconductor die on a substrate (e.g., aleadframe, a PCB, a carrier, a semiconductor chip, a semiconductorwafer, a BGA substrate, a semiconductor element, etc.), a packagedsemiconductor device, a flip chip semiconductor device, a die embeddedin a substrate, a stack of semiconductor die, amongst others. Further,the semiconductor element may include an element configured to be bondedor otherwise included in a semiconductor package (e.g., a spacer to bebonded in a stacked die configuration, a substrate, etc.).

As used herein, the term “substrate” is intended to refer to anystructure to which a semiconductor element may be bonded. Exemplarysubstrates include, for example, a leadframe, a PCB, a carrier, amodule, a semiconductor chip, a semiconductor wafer, a BGA substrate,another semiconductor element, etc.

In accordance with certain exemplary embodiments of the invention, afluxless bonding system is provided using reducing gas/gases. Thebonding system may be, for example, a flip chip bonding system, athermocompression bonding system, a thermosonic bonding system, etc.

Aspects of the invention relate to a novel fluxless chip-to-substrate orchip-to-wafer system that avoids oxidation of metal and solder padsduring bonding (e.g., during thermocompression bonding).

Exemplary systems include a “substrate oxide reduction chamber” (alsoreferred to as a substrate cleaning compartment), a “substrate oxideprevention chamber” (also referred to as a substrate protectioncompartment), and a “reducing gas delivery system” (e.g., a localizedchip and substrate oxide reduction bond head shroud, or other reducinggas delivery system) to eliminate the use of a fluxing process.

FIG. 1A illustrates exemplary bonding system 300. Bonding system 300includes: a substrate source 300 a (e.g., a wafer handler or othersource) for providing a substrate(s) 104 (such as a wafer, a printedcircuit board, etc.) on a support structure 300 a 1; and a processingsystem 300 b. Substrate 104 is configured to be transferred toprocessing system 300 b (e.g., including a tunnel 302, but may be adifferent type of structure). Tunnel 302 (or other structure, asdesired) includes a substrate oxide reduction chamber 302 a, a substrateoxide prevention chamber 302 b, and a bonding location 302 c (which ispart of substrate oxide prevention chamber 302 b). A reducing gasdelivery system 308 is also included in processing system 300 b.

In the example shown in FIG. 1A, because tunnel 302 includes bothsubstrate oxide reduction chamber 302 a and a substrate oxide preventionchamber 302 b, at least a portion of substrate oxide reduction chamber302 a has a common boundary with substrate oxide prevention chamber 302b. Substrate oxide reduction chamber 302 a is closed using entry door302 a 1 (which closes opening 302 a 1 a) and exit door 302 a 2 (whichcloses opening 302 a 2 a). Another reducing gas delivery system 302 d(which may be interconnected with reducing gas delivery system 308 touse a common source of reducing gas) is provided to provide a reducinggas (e.g., formic acid vapor) in substrate oxide reduction chamber 302a. After processing (e.g., removal of oxides from conductive structuresof substrate 104) in substrate oxide reduction chamber 302 a, asubstrate transfer system (which may be part of a material handlingsystem including support structure 102) is used to transfer substrate104 through exit door 302 a 2 to substrate oxide prevention chamber 302b. Substrate oxide prevention chamber 302 b includes an inertenvironment 306 (e.g., through a nitrogen supply, not shown forsimplicity). A material handling system (e.g., including supportstructure 102) is used to move substrate 104 within substrate oxideprevention chamber 302 b to a bonding location 302 c. While at bondinglocation 302 c, a reducing gas 130 is provided by reducing gas deliverysystem 308.

FIG. 1A also illustrates bond head assembly 106, including heater 108,and bonding tool 110. FIG. 1A also illustrates main exhaust 304 whichpulls exhaust gases (e.g., gases such as reducing gas vapors) throughpiping 304 a and 114 b 1 (where piping 114 b 1 is coupled, directly orindirectly, to center channel 114 b described below). Bond head assembly106 carries a bond head manifold 114 for receiving and distributingfluids (e.g., gases, vapors, etc.) as desired in the given application.Details of an exemplary bond head assembly 106, including exemplary bondhead manifold 114, are described below in connection with FIGS. 4-9, andFIGS. 10A-10D.

In connection with a bonding operation, semiconductor element 112 isbonded to substrate 104 using bonding tool 110. During the bondingoperation, corresponding ones of electrically conductive structures ofsemiconductor element 112 are bonded (e.g., using heat, force,ultrasonic energy, etc.) to respective ones of electrically conductivestructures of substrate 104. Bond head manifold 114 provides a reducinggas 130 (e.g., where the reducing gas is a saturated vapor gas) in thearea of semiconductor element 112 and substrate 104 in connection with abonding operation. After reducing gas 130 is distributed in the area ofsemiconductor element 112 and substrate 104, reducing gas 130 contactssurfaces of each of electrically conductive structures of semiconductorelement 112 and substrate 104.

FIG. 1B illustrates exemplary bonding system 400, which is similar inmany respect to bonding system 300 of FIG. 1A (where like elements havethe same reference numerals, or a numeral beginning with a “4” insteadof a “3”). Bonding system 400 includes a substrate source 400 a (e.g., awafer handler or other source) for providing a substrate(s) 104 (such asa wafer, a printed circuit board, etc.) on a support structure 400 a 1.Substrate 104 is configured to be transferred to processing system 400 b(e.g., including a tunnel 402, but may be a different type ofstructure). Tunnel 402 (or other structure, as desired) includes asubstrate oxide reduction chamber 402 a, a substrate oxide preventionchamber 402 b, and a bonding location 402 c (which is part of substrateoxide prevention chamber 402 b).

In the example shown in FIG. 1B, because tunnel 402 includes bothsubstrate oxide reduction chamber 402 a and a substrate oxide preventionchamber 402 b, at least a portion of substrate oxide reduction chamber402 a has a common boundary with substrate oxide prevention chamber 402b. A reducing gas delivery system 408 is also included in processingsystem 400 b. Substrate oxide reduction chamber 402 a is closed usingentry door 402 a 1 (which closes opening 402 a 1 a) and exit door 402 a2 (which closes opening 402 a 2 a). Another reducing gas delivery system402 d (which may be interconnected with reducing gas delivery system 408to use a common source of reducing gas) is provided to provide areducing gas (e.g., formic acid vapor) in substrate oxide reductionchamber 402 a. After processing (e.g., removal of oxides from conductivestructures of substrate 104) in substrate oxide reduction chamber 402 a,a substrate transfer system (which may be part of a material handlingsystem including support structure 102) is used to transfer substrate104 through opening 402 a 2 a to substrate oxide prevention chamber 402b. Substrate oxide prevention chamber 402 b includes an inertenvironment 406 (e.g., through a nitrogen supply, not shown forsimplicity). A material handling system (e.g., including supportstructure 102) is used to move substrate 104 within substrate oxideprevention chamber 402 b to a bonding location 402 c. While at bondinglocation 402 c, a reducing gas 130 is provided by reducing gas deliverysystem 408.

FIG. 1B also illustrates bond head assembly 106, including heater 108,and bonding tool 110. FIG. 1B also illustrates main exhaust 404 whichpulls exhaust gases (e.g., gases such as reducing gas vapors) throughpiping 404 a and 404 b. A manifold 214 is provided for receiving anddistributing fluids (e.g., gases, vapors, etc.) as desired in the givenapplication. Details of an exemplary bond head assembly 106, and anexemplary manifold 214, are described below in connection with FIGS.11A-11D).

In connection with a bonding operation, semiconductor element 112 isbonded to substrate 104 using bonding tool 110. During the bondingoperation, corresponding ones of electrically conductive structures ofsemiconductor element 112 are bonded (e.g., using heat, force,ultrasonic energy, etc.) to respective ones of electrically conductivestructures of substrate 104. Manifold 214 provides a reducing gas 130(e.g., where the reducing gas is a saturated vapor gas) in the area ofsemiconductor element 112 and substrate 104 in connection with a bondingoperation. After reducing gas 130 is distributed in the area ofsemiconductor element 112 and substrate 104, reducing gas 130 contactssurfaces of each of electrically conductive structures of semiconductorelement 112 and substrate 104.

FIG. 2A-2G illustrate a method of bonding a semiconductor element 112 toa substrate 104 in connection with an exemplary embodiment of theinvention, using bonding system 300 shown in FIG. 1A. FIG. 2Aillustrates a substrate 104 in substrate source 300 a, with entry door302 a 1 in an open position. Substrate oxide reduction chamber 302 a andsubstrate oxide prevention chamber 302 b have an inert environment 306(e.g., a nitrogen environment). At FIG. 2B, substrate 104 has been movedinto substrate oxide reduction chamber 302 a through opening 302 a 1 ausing a substrate handling system (e.g., a material handling systemincluding support structure 102). At FIG. 2C, entry door 302 a 1 isclosed, and a reducing gas 130 (e.g., formic acid vapor) is provided insubstrate oxide reduction chamber 302 a via reducing gas delivery system302 d. Reducing gas 130 removes residual oxide from the metal and solderpads (i.e., conductive structures) on substrate 104. At FIG. 2D, exitdoor 302 a 2 is opened, and substrate 104 is transferred from substrateoxide reduction chamber 302 a to substrate oxide prevention chamber 302b as shown in FIG. 2E. Substrate oxide prevention chamber 302 b includesan inert environment 306 (e.g., a nitrogen environment). In FIG. 2F,substrate 104 has been moved (e.g., using a material handling systemincluding support structure 102) to bonding location 302 c. At bondinglocation 302 c, a reducing gas 130 is directed from bond head manifold114 toward semiconductor element 112 and substrate 104. This reducinggas 130 is provided during bonding of semiconductor element 112 tosubstrate 104 to reduce/remove oxides on semiconductor element 112 aswell as any remaining residual oxides on substrate 104. At FIG. 2G,semiconductor element 112 has been bonded to substrate 104 using bondhead assembly 106.

Although FIGS. 2A-2G illustrate bonding system 300, it is contemplatedthat a substantially similar process could be applied to bonding system400 shown in FIG. 1B, or other bonding systems within the scope of theinvention.

While the exemplary process of FIGS. 2A-2G illustrates a singlesubstrate 104, it is contemplated that a plurality of substrates 104 maybe involved in system 300 (or bonding system 400 of FIG. 1B) (or anotherbonding system within the scope of the invention). Thus, FIGS. 3A-3Billustrate multiple substrates 304. In FIG. 3A, a first substrate 304(already having been processed using substrate oxide reduction chamber302 a) is being moved to bonding location 302 c of substrate oxideprevention chamber 302 b. In FIG. 3B, while that substrate 304 is atbonding location 302 c, another substrate 304 is in substrate oxidereduction chamber 302 a (e.g., for cleaning of conductive structures onthe another substrate 304).

Exemplary aspects of the invention provides an opportunity to rework asubstrate 304 (e.g., to transfer the substrate back to substrate oxidereduction chamber 302 a). For example, such an approach might be usefulin situations where prolonged substrate exposures to heating isunavoidable, for example, bonding of small dies (e.g. 0.1-1 mm edgesize) to a large area (e.g. 200-300 mm diameter substrate).

The invention may provide a number of benefits such as, for example:fluxless bonding (e.g., no fluxing of the semiconductor element or thesubstrate is required prior to or during bonding); reduction of oxides(e.g., metal oxides such as Cu and Sn oxides formed on pads/bumps) onboth the semiconductor element and the substrate, as well as preventionof oxide formation during long heat exposures; a low consumption ofnitrogen gas (or other gas providing the inert environment in thesubstrate oxide prevention chamber); and a pre-cleaning chamber, aninert gas chamber, and an in-situ oxide cleaning bond head are allprovided in the same bonding system.

While it is not explicitly shown in FIG. 1, FIGS. 2A-2G, and FIGS.3A-3B, it is understood that a bonding operation may include bonding asemiconductor element 112 (or a plurality of elements) to a portion ofthe bond sites (bonding areas) of substrate 104 in the tunnel (e.g.,tunnel 302). For example, that portion of the bond sites of substrate104 may be exposed by an opening in the tunnel 302, where the bondingtool may be lowered through opening 302 e to complete the bondingoperation. By only exposing a portion of substrate 104 at a time, theenvironment within tunnel 302 is better maintained.

In connection with bonding (e.g., thermocompression bonding) of asemiconductor element 112 (including electrically conductive structures)to a substrate 104 (including electrically conductive structures), heatmay be provided through bonding tool 110 (e.g., from a heater of bondhead assembly 106). A reducing gas may also be provided for cleaningoxides and/or other contaminants on the surface of the electricallyconductive structures (of semiconductor element 112 and/or substrate104).

In specific examples of such methods, a semiconductor element 112 (e.g.,a semiconductor chip) is transferred from a source (e.g., asemiconductor wafer) to bonding tool 110 of a thermocompression bondingmachine or a flip chip bonding machine. With semiconductor element 112carried by bonding tool 110 (e.g., using vacuum), bond head assembly 106(carrying bonding tool 110) is moved to a desired bonding position. Thesemiconductor element 112 is bonded to the bonding position of substrate104 (e.g., while heating the semiconductor element 112 and/or thesubstrate 104) (e.g., where the bonding occurs in the presence of areducing gas). The respective conductive structures of the semiconductorelement 112, and/or the substrate 104 may include a solder material(e.g., the conductive structures may include a solder material at acontact surface, the conductive structures may be formed of a soldermaterial, etc.), or the conductive structures may be formed of anotherconductive material (e.g., copper).

Throughout the various drawings (including FIGS. 4-9, FIGS. 10A-10D, andFIGS. 11A-11D), like reference numerals refer to the like elements,except where explained herein.

Referring now to FIG. 4, a bonding machine 100 (e.g., a flip chipbonding machine, a thermocompression bonding machine, etc.) is provided.Bonding machine 100 includes a support structure 102 for supporting asubstrate 104 during a bonding operation (where substrate 104 includes aplurality of electrically conductive structures 104 a). Supportstructure 102 may include any appropriate structure for the specificapplication. In FIGS. 4-9 and FIGS. 10A-10D, support structure 102includes top plate 102 a (configured to directly support substrate 104),chuck 102 c, and heater 102 b disposed therebetween. In applicationswhere heat for heating substrate 104 is desirable in connection with thebonding operation, a heater such as heater 102 b may be utilized.

FIG. 4 also illustrates bond head assembly 106, which may be configuredto move along (and about) a plurality of axes of bonding machine 100such as, for example, the x-axis, y-axis, z-axis, theta (rotative) axis,etc. Bond head assembly 106 includes heater 108 and bonding tool 110.That is, in certain bonding machines (e.g., thermocompression bondingmachines) it may be desirable to heat the bonding tool. Thus, while FIG.4 illustrates a separate heater 108 for heating bonding tool 110 (forheating semiconductor element 112 including a plurality of electricallyconductive structures 112 a), it will be appreciated that heater 108 andbonding tool 110 may be integrated into a single element (e.g., a heatedbonding tool).

In connection with a bonding operation, semiconductor element 112 isbonded to substrate 104 using bonding tool 110. During the bondingoperation, corresponding ones of electrically conductive structures 112a are bonded (e.g., using heat, force, ultrasonic energy, etc.) torespective ones of electrically conductive structures 104 a. In FIG. 4,electrically conductive structures 112 a include a solder material 112 a1 at a contact portion of each electrically conductive structure 112 a(e.g., a portion configured to contact the electrically conductivestructures 104 a of semiconductor element 104).

In certain bonding applications (e.g., flip chip and/orthermocompression bonding with copper conductive structures), it isdesirable to provide an environment suitable for bonding.Conventionally, such an environment may be provided by using a reducinggas at the bonding area to reduce potential contamination of theelectrically conductive structures of the semiconductor element or thesubstrate to which it will be bonded.

In FIG. 4, bond head assembly 106 carries a bond head manifold 114 forreceiving and distributing fluids (e.g., gases, vapors, etc.) as desiredin the given application. In FIG. 4, while bond head manifold 114 isillustrated in a cross sectional view, the actual bond head manifold 114surrounds bonding tool 108 (e.g., bond head manifold 114 surroundsbonding tool 108 in a coaxial configuration). Of course, bond headmanifold 114 may have different configurations from that shown in FIG.4. Further, it is understood that certain details of bond head manifold114 (e.g., interconnection with piping 120, structural details fordistributing a reducing gas within bond head manifold 114, structuraldetails for distributing a shielding gas within bond head manifold 114,structural details for drawing a vacuum through a center channel of bondhead manifold 114, etc.) are omitted for simplicity.

Bond head manifold 114 includes three channels 114 a, 114 b, 114 chaving different functions. Outer channel 114 a receives a shielding gas(e.g., nitrogen gas) from shielding gas supply 118. That is, a shieldinggas is provided from shielding gas supply 118 (e.g., a nitrogen supply),through piping 120 (where piping 120 may include hard piping, flexibletubing, a combination of both, or any other structure adapted to carrythe fluids described herein), to outer channel 114 a of bond headmanifold 114. From outer channel 114 a of bond head manifold 114, theshielding gas 128 is provided as a shield from the outside environment(e.g., see FIGS. 10B-10C).

Inner channel 114 c receives a reducing gas 130 (e.g., see FIGS.10B-10C) (e.g., where the reducing gas is a saturated vapor gas) viapiping 120, and provides reducing gas 130 in the area of semiconductorelement 112 and substrate 104 in connection with a bonding operation.Reducing gas 130 is provided by a vapor generation system 122, butinitiates as reducing gas 126. In the example shown in FIG. 4, vaporgeneration system 122 is a bubbler type system including an acid fluid124 (e.g., formic acid, acetic acid, etc.) in vessel 122 a of thebubbler type system. A carrier gas (e.g., nitrogen) is provided (viapiping 120) into acid fluid 124 in vessel 122 a, where the carrier gasacts as a carrier for the acid fluid 124. Collectively, the carrier gas(e.g., nitrogen) and acid fluid 124 are transported as reducing gas 126.Within piping 120, additional carrier gas (e.g., nitrogen) may be addedto reducing gas 126 (e.g., to vary the concentration of the reducinggas, as desired) via piping section 120 a, thereby providing reducinggas 130 in the area of semiconductor element 112 and substrate 104 inconnection with the bonding operation. After reducing gas 130 isdistributed in the area of semiconductor element 112 and substrate 104,reducing gas 130 contacts surfaces of each of electrically conductivestructures 104 a and electrically conductive structures 112 a (e.g., seeFIG. 10B). The surfaces of electrically conductive structures 104 a/112a may then include a reaction product (e.g., where the reaction productis provided as a result of (i) a surface oxide on electricallyconductive structures 104 a/112 a, and (ii) reducing gas from reducinggas 130 (and possibly heat provided by heater 108 and transferred toelectrically conductive structures 104 a via contact with electricallyconductive structures 112 a, if desired). This reaction product isdesirably removed from the bonding area (i.e., the area whereelectrically conductive structures 112 a of semiconductor element 112are bonded to corresponding electrically conductive structures 104 a ofsubstrate 104) using vaccum provided through center channel 114 b ofbond head manifold 114 via exit piping 116.

Thus, FIG. 4 illustrates: (i) various elements of bonding machine 100;(ii) a path of carrier gas from carrier gas supply 118 to outer channel114 a of bond head manifold 114; (iii) a path of reducing gas 126 (whichmay receive additional carrier gas from piping 120) from vaporgeneration system 122 to inner channel 114 c of bond head manifold 114,where it is released to the bonding area as reducing gas 130; and (iv) apath of gas (which may carry away a reaction product from surfaces ofelectrically conductive structures 104 a/112 a) drawn by vacuum throughcenter channel 114 b of bond head manifold 114. The aforementioned pathsare illustrated in FIG. 4 through various arrows even though gas is notflowing in FIG. 4 (see FIGS. 10A-10D for an exemplary operation).

FIG. 5 again illustrates bonding machine 100 as shown in FIG. 4;however, in FIG. 5 electrically conductive structures 112 a do notinclude a solder material 112 a 1 as shown in FIG. 4. Rather, in FIG. 5,electrically conductive structures 104 a include a solder material 104 a1 at a contact portion of each electrically conductive structure 104 a(e.g., a portion configured to contact the electrically conductivestructures 112 a of semiconductor element 112).

FIG. 6 again illustrates bonding machine 100 as shown in FIGS. 4-5;however, in FIG. 6 electrically conductive structures 112 a include asolder material 112 a 1 as shown in FIG. 4, and electrically conductivestructures 104 a include a solder material 104 a 1 as shown in FIG. 5.

FIG. 7 again illustrates bonding machine 100 as shown in FIG. 4;however, in FIG. 7 electrically conductive structures 112 a (shown inFIG. 4) are replaced by electrically conductive structures 112 a 2 whichare formed of a solder material. That is, unlike FIG. 4, whereelectrically conductive structures 112 a includes a solder material 112a 1 at a contact portion, in FIG. 7, electrically conductive structures112 a 2 are fully formed of a solder material.

FIG. 8 again illustrates bonding machine 100 as shown in FIG. 5;however, in FIG. 8 electrically conductive structures 104 a (shown inFIG. 5) are replaced by electrically conductive structures 104 a 2 whichare formed of a solder material. That is, unlike FIG. 5, whereelectrically conductive structures 104 a includes a solder material 104a 1 at a contact portion, in FIG. 8, electrically conductive structures104 a 2 are fully formed of a solder material.

FIG. 9 again illustrates bonding machine 100 as shown in FIGS. 4-8;however, in FIG. 9 electrically conductive structures 112 a (shown inFIGS. 4 and 6, including a solder material 112 a 1) are replaced byelectrically conductive structures 112 a 2 (fully formed of a soldermaterial) as shown in FIG. 7. Further, in FIG. 9, electricallyconductive structures 104 a (shown in FIG. 5, including a soldermaterial 104 a 1) are replaced by electrically conductive structures 104a 2 (fully formed of a solder material) as shown in FIG. 8.

Thus, according to certain aspects of the invention the electricallyconductive structures of the semiconductor element being bonded, or thesubstrate configured to receive the semiconductor element during bonded,may include a solder material. The solder material may be included in anumber of different configurations. For example, the solder material maybe included at a contact portion of the electrically conductivestructures (e.g., see FIGS. 4-6). In another non-limiting example, theentire electrically conductive structures may be formed of the soldermaterial (e.g., see FIGS. 7-9).

FIGS. 10A-10D and FIGS. 11A-11D are block diagrams illustrating methodsof bonding a semiconductor element to a substrate. In each of FIGS.10A-10D and FIGS. 11A-11D: (i) the semiconductor element 112 (withelectrically conductive structures 112 a including solder material 112 a1 at a contact portion) is shown as in FIG. 4; and (ii) the substrate104 (with electrically conductive structures 104 a not including asolder material) is shown as in FIG. 4. However, it is understood thatthe methods shown and described with respect to FIGS. 10A-10D and FIGS.11A-11D are equally applicable to the semiconductor elements andsubstrates of each of FIGS. 4-9, and are applicable to the semiconductorelements and substrates of any other embodiment within the scope of theinvention.

Prior to the processes shown and described in connection with FIGS.10A-10D and FIGS. 11A-11D, semiconductor element 112 and/or substrate104 may be “cleaned”. For example, the electrically conductivestructures 112 a, 104 a of one or both of semiconductor element 112 andsubstrate 104 may be cleaned using a solution such as hydrochloric acidor acetic acid. Such a cleaning step may be performed, for example, bydipping at least a portion of semiconductor element 112 and/or substrate104 into such a solution.

Referring now to FIG. 10A, semiconductor element 112 (carried by bondhead 106) is positioned above substrate 104. As shown in FIG. 10B, vaporgeneration system 122 has been activated to produce reducing gas 130 atthe bonding area. More specifically, FIG. 10B illustrates reducing gas130 being provided at the bonding area, as well as shielding gas 128being provided, and vacuum being drawn through center channel 114 b ofbond head manifold 114 via exit piping 116. Thus, the flow of reducinggas 130 reach desired portions of semiconductor element 112 andsubstrate 104 (e.g., electrically conductive structures 104 a andelectrically conductive structures 112 a) for: removing contaminantsfrom the electrically conductive structures 104 a and electricallyconductive structures 112 a; and/or shielding electrically conductivestructures 104 a and electrically conductive structures 112 a fromfurther potential contamination.

Also shown in FIG. 10B, respective ones of electrically conductivestructures 112 a (of semiconductor element 112) are aligned with ones ofelectrically conductive structures 104 a (of substrate 104). At FIG.10C, the process proceeds to a bonding step (e.g., a thermocompressionbonding step), for example, through the lowering of bond head 106. Thatis, electrically conductive structures 112 a are bonded to correspondingelectrically conductive structures 104 a. This may be through athermocompression bonding process (e.g., including heat and/or bondforce, where the bond force may be a higher bond force such as 50-300N), and may also include ultrasonic energy transfer (e.g., from anultrasonic transducer included in bond head assembly 106). At FIG. 10D,the bonding process has been completed. That is, semiconductor element112 has been bonded to substrate 104, such that correspondingelectrically conductive structures 112 a, 104 a are now bonded to oneanother with deformed solder material 112 a 1 provided therebetween.

Although FIGS. 10A-10D (and FIGS. 4-9) illustrate manifold 114,integrated with the bond head, for: delivering the reducing gas;delivering the shielding gas; and providing vacuum—the invention is notlimited thereto. For example, instead of such functions being providedthrough integration of a manifold with the bond head assembly, suchfunctions may be provided through integration with a support structurefor supporting the substrate. Further, such functions may be splitbetween the bond head assembly and the support structure (and possiblyother structures of the bonding machine). FIGS. 11A-11D are a series ofblock diagrams of a bonding machine 100″, with certain similar elementsand functions to that illustrated and described with respect to FIG. 4and FIGS. 10A-10D, except that the manifold functions (delivering thereducing gas; delivering the shielding gas; and providing vacuum) areintegrated into a support structure 202.

FIG. 11A illustrates bonding machine 100″ (e.g., a flip chip bondingmachine, a thermocompression bonding machine, etc.). Bonding machine100″ includes a support structure 202 for supporting a substrate 104during a bonding operation (where substrate 104 includes a plurality ofelectrically conductive structures 104 a). Support structure 202 mayinclude any appropriate structure for the specific application. In FIGS.11A-11D, support structure 202 includes top plate 202 a (configured todirectly support substrate 104), chuck 202 c, and heater 202 b disposedtherebetween. In applications where heat for heating substrate 104 isdesirable in connection with the bonding operation, a heater such asheater 202 b may be utilized.

FIG. 11A also illustrates bond head assembly 106 (including heater 108and bonding tool 110), which may be configured to move along (and about)a plurality of axes of bonding machine 100″ such as, for example, thex-axis, y-axis, z-axis, theta (rotative) axis, etc. In FIG. 11A, bondhead assembly 106 carries a plate 107 for partially containing at leastone of shielding gas 128 and reducing gas 130 (see description below).

As opposed to a bond head manifold 114 carried by bond head assembly 106(as in FIGS. 10A-10D), FIGS. 11A-11I illustrate a manifold 214 carriedby, and/or intergrated with, support structure 202. Manifold 214 isconfigured for receiving and distributing fluids (e.g., gases, vapors,etc.) as desired in the given application. In FIG. 11A, while manifold214 is illustrated in a cross sectional view, the actual manifold 214 atleast partially surrounds substrate 104. Of course, manifold 214 mayhave different configurations from that shown in FIG. 11A. Further, itis understood that certain details of manifold 214 (e.g.,interconnection with piping 120, structural details for distributingreducing gas 130 within manifold 214, structural details fordistributing shielding gas 128 within manifold 214, structural detailsfor drawing a vacuum through a center channel of manifold 214, etc.) areomitted for simplicity.

Manifold 214 includes three channels 214 a, 214 b, 214 c havingdifferent functions. Outer channel 214 a receives shielding gas 128(e.g., nitrogen gas) from shielding gas supply 118 via piping 120. Fromouter channel 214 a of manifold 214, shielding gas 128 is provided as ashield from the outside environment (e.g., see FIGS. 11B-11C). Innerchannel 214 c receives a reducing gas 130 (e.g., see FIGS. 11B-11C)(e.g., where the reducing gas is a saturated vapor gas) via piping 120,and provides reducing gas 130 in the area of semiconductor element 112and substrate 104 in connection with a bonding operation. Reducing gas130 is provided by a vapor generation system 122, but initiates asreducing gas 126 (e.g., see description above with respect to FIG. 4).After reducing gas 130 is distributed in the area of semiconductorelement 112 and substrate 104, reducing gas 130 contacts surfaces ofeach of electrically conductive structures 104 a and electricallyconductive structures 112 a. The surfaces of electrically conductivestructures 104 a/112 a may then include a reaction product (e.g., wherethe reaction product is provided as a result of: (i) a surface oxide onelectrically conductive structures 104 a/112 a, and (ii) reducing gasfrom reducing gas 130 (and possibly heat provided by heater 108, ifdesired). This reaction product is desirably removed from the bondingarea (i.e., the area where electrically conductive structures 112 a ofsemiconductor element 112 are bonded to corresponding electricallyconductive structures 104 a of substrate 104) using vacuum providedthrough center channel 214 b of manifold 214 via exit piping 216.

Thus, FIG. 11A illustrates: (i) various elements of bonding machine100″; (ii) a path of carrier gas from carrier gas supply 118 to outerchannel 214 a of manifold 214; (iii) a path of reducing gas 126 (whichmay receive additional carrier gas from piping 120 a) from vaporgeneration system 122 to inner channel 214 c of manifold 214, where itis released to the bonding area as reducing gas 130; and (iv) a path ofgas (which may carry away a reaction product from surfaces ofelectrically conductive structures 104 a/112 a) drawn by vacuum throughcenter channel 214 b of manifold 214. The aforementioned paths areillustrated in FIG. 11A through various arrows even though gas is notflowing in FIG. 11A.

Referring now to FIG. 11A, semiconductor element 112 (carried by bondhead 106) is positioned above substrate 104. As shown in FIG. 11B, vaporgeneration system 122 has been activated to produce reducing gas 130 atthe bonding area. More specifically, FIG. 11B illustrates reducing gas130 being provided at the bonding area, as well as shielding gas 128being provided, and vacuum being drawn through center channel 114 b ofbond head manifold 114 via exit piping 116. Thus, the flow of reducinggas 130 reach desired portions of semiconductor element 112 andsubstrate 104 (e.g., electrically conductive structures 104 a andelectrically conductive structures 112 a) for: removing contaminantsfrom the electrically conductive structures 104 a and electricallyconductive structures 112 a; and/or shielding electrically conductivestructures 104 a and electrically conductive structures 112 a fromfurther potential contamination.

Also shown in FIG. 11B, respective ones of electrically conductivestructures 112 a (of semiconductor element 112) are aligned with ones ofelectrically conductive structures 104 a (of substrate 104). At FIG.11C, the process proceeds to a bonding step (e.g., a thermocompressionbonding step), for example, through the lowering of bond head 106. Thatis, electrically conductive structures 112 a are bonded to correspondingelectrically conductive structures 104 a. This may be through athermocompression bonding process (e.g., including heat and/or bondforce, where the bond force may be a higher bond force such as 50-300N), and may also include ultrasonic energy transfer (e.g., from anultrasonic transducer included in bond head assembly 106). At FIG. 11D,the bonding process has been completed. That is, semiconductor element112 has been bonded to substrate 104, such that correspondingelectrically conductive structures 112 a, 104 a are now bonded to oneanother with deformed solder material 112 a 2 provided therebetween.

Although the invention has been illustrated primarily with respect toone of manifolds 114, 214 for directing (i) the flow of reducing gas130, (ii) the flow of shielding gas 128, and (iii) the pull of thevacuum, it is understood that the structure used to direct the flowpatterns may be different from that illustrated. That is, theconfiguration of the structure used to provide and direct fluids 130,128 (and to draw vacuum) may vary considerably from that shown.

The invention described herein in connection with FIGS. 4-9, FIGS.10A-10D, and FIGS. 11A-11D may provide a number of benefits such as, forexample: fluxless bonding (e.g., no fluxing of the semiconductor elementor the substrate is required prior to or during bonding); reduction ofoxides on both the semiconductor element and the substrate; amongothers.

It will be appreciated by those skilled in the art that certain elementsof bonding machine 100 (see FIGS. 4-9 and FIGS. 10A-10D), and/or bondingmachine 100″ (see FIGS. 11A-11D) may be integrated into the systems ofFIG. 1, FIGS. 2A-2G, and FIGS. 3A-3B, to replace at least a portion ofthe elements of the bondhead compartments (e.g., the bond head, theshroud, certain piping, etc.).

Although the invention has been described and illustrated with respectto the exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, without partingfrom the spirit and scope of the present invention. Rather, variousmodifications may be made in the details within the scope and range ofequivalents of the claims and without departing from the invention.

1. A method of bonding a semiconductor element to a substrate, themethod comprising the steps of: moving a substrate into a substrateoxide reduction chamber, the substrate including a plurality of firstelectrically conductive structures, the substrate oxide reductionchamber configured to receive a reducing gas to contact each of theplurality of first electrically conductive structures; moving thesubstrate into a substrate oxide prevention chamber after the reducinggas contacts the plurality of first electrically conductive structures,the substrate oxide prevention chamber having an inert environment whenreceiving the substrate; and providing a reducing gas environment duringbonding of a semiconductor element to the substrate, the semiconductorelement including a plurality of second electrically conductivestructures, the plurality of first electrically conductive structuresbeing configured to be bonded with corresponding ones of the pluralityof second electrically conductive structures.
 2. A method of bonding asemiconductor element to a substrate, the method comprising the stepsof: (a) carrying a semiconductor element with a bonding tool of abonding machine, the semiconductor element including a plurality offirst electrically conductive structures; (b) supporting a substratewith a support structure of the bonding machine, the substrate includinga plurality of second electrically conductive structures; (c) providinga reducing gas in contact with each of the plurality of firstelectrically conductive structures and the plurality of secondelectrically conductive structures; and (d) bonding the correspondingones of the plurality of first electrically conductive structures to therespective ones of the plurality of second electrically conductivestructures after step (c), wherein at least one of the plurality offirst electrically conductive structures and the plurality of secondelectrically conductive structures includes a solder material.
 3. Themethod of claim 2 wherein each of the plurality of first electricallyconductive structures and the plurality of second electricallyconductive structures includes solder material.
 4. The method of claim 2wherein at least one of the plurality of first electrically conductivestructures and the plurality of second electrically conductivestructures includes solder material at a contact portion thereof.
 5. Themethod of claim 2 wherein the plurality of first electrically conductivestructures includes solder material at a contact portion thereof.
 6. Themethod of claim 2 wherein the plurality of second electricallyconductive structures includes solder material at a contact portionthereof.
 7. The method of claim 2 wherein both of the plurality of firstelectrically conductive structures and the plurality of secondelectrically conductive structures includes solder material at a contactportion thereof.
 8. The method of claim 2 wherein at least one of theplurality of first electrically conductive structures and the pluralityof second electrically conductive structures is formed of soldermaterial.
 9. The method of claim 2 wherein the plurality of firstelectrically conductive structures are formed of solder material. 10.The method of claim 2 wherein the plurality of second electricallyconductive structures are formed of solder material.
 11. The method ofclaim 2 wherein both of the plurality of first electrically conductivestructures and the plurality of second electrically conductivestructures are formed of solder material.
 12. The method of claim 2wherein the reducing gas includes a carrier gas and an acid.
 13. Themethod of claim 12 wherein the acid includes one of formic acid andacetic acid.
 14. The method of claim 2 wherein the reducing gas is asaturated vapor gas provided via a vapor generation system included onthe bonding machine.
 15. The method of claim 2 wherein step (d) includesapplying ultrasonic energy between the semiconductor element and thesubstrate.
 16. The method of claim 2 wherein step (d) includes bondingthe corresponding ones of the plurality of first electrically conductivestructures to the respective ones of the plurality of secondelectrically conductive structures through a thermocompression bondingprocess.
 17. The method of claim 2 wherein the bonding tool is carriedby a bond head of the bonding machine, and wherein step (c) includesproviding the reducing gas in contact with each of the plurality offirst electrically conductive structures and the plurality of secondelectrically conductive structures via a manifold integrated with thebond head.
 18. The method of claim 2 wherein step (c) includes providingthe reducing gas in contact with each of the plurality of firstelectrically conductive structures and the plurality of secondelectrically conductive structures via a manifold integrated with thesupport structure.
 19. The method of claim 2 wherein the bonding machineincludes a fluxless bonding system.
 20. The method of claim 2 whereinthe bonding machine includes at least one of a flip chip bonding system,a thermocompression bonding system, and a thermosonic bonding system.